Recently, technologies have arisen that allow near field coupling (e.g., wireless power transfers (WPT) and near field communications (NFC)) between mobile devices in close proximity to each other. Such near field coupling functions may use radio frequency (RF) antennas in the devices to transmit and receive electromagnetic signals. Because of user desires (and/or for esthetic reasons) many of these mobile or portable devices are small (and becoming smaller), and tend to have exaggerated aspect ratios when viewed from the side. As a result, many of these mobile devices incorporate flat antennas, which use coils of conductive material as their radiating antennas for use in near field coupling functions.
Most mobile devices such as cellular phones, pad and tablet computers, laptops, and Ultrabooks use metal chassis for providing robust mechanical strength, and for improved protection against electromagnetic interference (EMI) and/or electromagnetic static discharge (ESD). However, electromagnetic coupling between the two NFC antennas of the mobile devices to communicate with one another may degrade significantly if metal is present between the two antennas. This is due to the fact that metal acts as a shield and Eddy currents may be induced in the metal.
To improve communications coupling between the two NFC antennas, a conventional solution is to remove a conductive (or metal) coating and/or introduce a large cutout area in the metal chassis, thereby removing the shield for the magnetic field. However, the conventional solution while attempting to improve the coupling between the two NFC antennas also creates an unwanted reduction in the robustness of the mobile device and causes deterioration in the EMI/ESD performance of the mobile device. In addition, having a large cutout area in the conductive coating may not be a feasible option for many smaller sized mobile devices such as smartphones and Ultrabooks. Accordingly, there is a need for an improved NFC antenna configuration.
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